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robert1107
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(Non-Commercial) DC to AC Invertors That Will Handle Inductive Loads

06/12/2008 11:19 PM

My research is purely academic. I am interested in renewable energy systems and wondered if when installing P.V. array/regulator/battery that a DC 48Volt invertor to produce 240V (U.K.) would possibly be able to handle inductive loads, I understand that inductive loads, say for example on fluorescent lighting, produce large back EMF, with resulting damage to power transistors/etc and I wondered how commercially designed systems get round this. Is it just a simple matter of increasing peak voltage handling of power transistors or more complex?
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YWROADRUNNER
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#1

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/12/2008 11:55 PM

I don't believe there will be a problem handling inductive loads, however the subject has been discussed many times before, I will include a link to at least one of the blogs.

http://cr4.globalspec.com/thread/16468#comment171169

Elnav is particularly knowledgeable in this area, I'm sure you could p.m. him if you can't find the information you're looking for.

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robert1107
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#2
In reply to #1

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/13/2008 1:54 AM

Thanks YWROADRUNNER for fast and accurate reply on above.

All this is relevant to inverters, I was remembering about DC to DC converters and if memory serves me right these were based on large value electrolytics in series or something, now thinking of a television switched mode power supply with monostable based pulse width modulated feedback system, would there be any way of running the standard inverter system as normal but feedback would be monitored for higher voltage spike, when this is detected (CPU sensor) the switched mode dumps all the higher voltage into an capacitor-inductor network while switching the inverter out-of-circuit, once CPU sensor monitors normal voltage again, the inverter could be switched back in circuit.
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marcot
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#3
In reply to #2

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/14/2008 12:31 PM

The problems and difficulties you are describing have been solved by most equipment vendors that have been around long enough. Bad things sometimes happens to people buying prototypes. Use reputable suppliers, don't just compare prices, and you won't have to worry about the details of a technology you don't completely understand. This will release you to invest your time into your application.

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robert1107
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#9
In reply to #3

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/15/2008 9:43 PM

thanks Marcot for your help and time,

best regards

robert1107
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elnav
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#4
In reply to #2

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/14/2008 3:27 PM

Hello Robert1107 - as noted by other poster most mainstream commercial suppliers of inverter have already solved that problem. Something not often advertised is the fact toroidal high frequency switched inverters are better able to handle the large surges caused by inductive loads. It used to be the conventional wisdom said you could not drive large inductive laods with inverters. Not true! You can and I proved it back in 2003. Now I see several major brand name suppliers of air conditioning advertising inverter driven air conditioning units.

Admittedly some of this development was enabled by the large scale availability of isolated gate bipolar transistors or IGBT for short. Today the big problem is too much demand and too little supply. Several users tell me they are back ordered for weeks or months.

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YWROADRUNNER
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#5
In reply to #4

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/14/2008 4:13 PM

Hello elnav

Speaking of inverter driven AC units, I recently replaced several 480 V VFD's on a job with fan coils. The VFD's I remove are actually fairly new models in good condition.

I haven't gotten around to calling the manufacture but perhaps you would have some information. In the past I've put single phase into a VFD and gotten three phase out at a reduced rating of course. What I'm thinking here is it possibly by replacing the control transformer(or it might not be necessary) and reprogramming the drive I could get it to operate on 220 V.

Several times in the past having 220 V three phase available in my garage would've come in handy, (a lot of times you can pick up shop equipment that's three phase etc. for next to nothing) not to mention the novelty of having a VFD to play with in my garage.

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elnav
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#6
In reply to #5

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/14/2008 5:20 PM

Sorry roadrunner. I am not intimately familiar with VFD technology. I do not think all VFD will deliver 3 phase from a single phase source. In order to do so you need three output modules which are synchronized by a clock circuit and phase locked to the master unit. I know of one company that does that kind of thing as a universal power converter for yachts. their competitor uses a well known brand of VFD and lock it down to one speed that corresponds to a 60HZ or a 50Hz output. In that way they converte an alien input frequency and voltage to the desired output voltage and frequency required by th eon board equipment.

the difference between the two brands is single conversion versus doubel conversion. Doubel being the better way with mopre control and flexibility.

If it is your intent to gang three VFD together into a 3 phase setup yo uneed to access the control board and bring ou tth es=ynchronizing clock signal and then tie the other two so as to remain 120 degrees out of phase in a stabel configuration.

Only the manufacturer can telll you if that particular model is designed to do that. As for the voltage, yes a simple transformer 2:1 step down wil do that. I have a 3 phase 26 volt 400Hz drive but needed 120V for driving a particular aircraft device.

Adding three cheap transformers 24V: 120V did the trick. Just wach your KVA rating and the physical orientation since some transformers will inductively couple to each other when mounted in close proximity. Unlike a commecial 3 ph transformer with the coils already mounted in a fixed relationship to each other as determined by the coore laminations using independent transformers allow so misalignment.

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YWROADRUNNER
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#7
In reply to #6

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/14/2008 7:37 PM

Well hopefully next week my memory will not fail and I will call the manufacture, I'll let you know what they say. I've had many chances over the years to pickup motors for nothing and machine shop equipment for next to nothing but I passed on them for lack of three phase power.

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elnav
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#8
In reply to #7

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/14/2008 7:51 PM

you could also have gotten a rotary converter. not as efficient but does work. Its motor driving a generator. Depending on how you want it you can get single phase in, 3 PH out or vice versa. and of course get a voltage conversion as well depending on how the units are wound.

My buddy helped his kid set up a machine shop as a start up business. They found a whole slew of manual control machinery all of it 3 ph but dirt cheap. Basically scrap metal pricing. Unfortunately the industrial mall complex did not have 3 ph power so we swapped out a lot of motors. Fortunately there was enough power available since the load and power factor was shot all to H*** with converting to single phase. But it did work.

This was back before big hi power inverters were readily available. In those days a 1000 watt inverter was considerd good and 2000 watts was humongous.

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robert1107
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#10
In reply to #4

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/15/2008 9:58 PM

thanks elnav for your reply.

you say that IGBT (isolated gate bipolar transistor) are available but difficult to get for this very useful piece of equipment, would a TRIAC or DIAC be something that would be interchangeable, or possibly this may have been tried and could either not switch fast enough or may not have the power capacity. I'm stretching the limits of my understanding of this concept as my previous jobs in this field did not go into prototypes.

Kind regards

robert1107
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elnav
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#11
In reply to #10

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/15/2008 10:58 PM

in a word NO! Triacs and diacs belong to a much earlier stage of technology development. I am not aware of anyone stil using them.

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robert1107
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#12
In reply to #11

Re: (non commercial) DC to AC invertors that will handle inductive loads

06/15/2008 11:18 PM

thanks again elnav for your help.

Kind regards

robert1107.
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PWSlack
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#13

Re: (Non-Commercial) DC to AC Invertors That Will Handle Inductive Loads

06/19/2008 7:58 AM

Well, caravan and marine equipment stores sell battery-to-240vac inverters.

Reinvention of the proverbial wheel is rarely necessary...

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robert1107
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#14
In reply to #13

Re: (Non-Commercial) DC to AC Invertors That Will Handle Inductive Loads

06/19/2008 10:45 PM

Thanks PWSlack,

I will check this out.

Best wishes

Robert1107.
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elnav
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#15
In reply to #14

Re: (Non-Commercial) DC to AC Invertors That Will Handle Inductive Loads

06/19/2008 10:59 PM

Robert, it isn't clear where you are located. However Victron is a dutch company with a growing presence in North America. they make both 120V and 230V inverter and charger and combination units. On their website they have news worthy picturs of significant installations. One recent addition shows a huge PV and inverter installation of around 50kW. It is a hostel high in the Spanish mountains. The whole complex is run by inverters and PV. From your original question it sounds like this is what you are wondering about. In my opinion Victron probably has th emost technically advanced product lineup.

www.victronenergy.com then look for news announcements.

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robert1107
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#16
In reply to #15

Re: (Non-Commercial) DC to AC Invertors That Will Handle Inductive Loads

06/19/2008 11:08 PM

Dear elnav,

Thanks again, everyone seems to communicate on CR4 real quick. I live near Edinburgh in Scotland United Kingdom.

Bye for now.
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